Stock Issued At Separation And Distribution From Former Parent, Shares

No definition available.

Name:	musa_StockIssuedAtSeparationAndDistributionFromFormerParentShares
Namespace Prefix:	musa_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_EquityClassOfTreasuryStockLineItems
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Balance Type:	na
Period Type:	duration

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

+ Details

Name:	us-gaap_TreasuryStockAcquiredAverageCostPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.28,29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30
-Article 5

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=musa_MayTwoThousandFourteenShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=musa_TwoHundredFiftyMillionDollarShareRepurchaseProgramMember
Namespace Prefix:
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Balance Type:
Period Type:

Earnings Per Share (Narrative) (Details) - USD ($)		1 Months Ended	12 Months Ended
Earnings Per Share (Narrative) (Details) - USD ($)	Aug. 30, 2013	May. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Issuance of stock at the separation and distribution, shares	46,743,316
Stock repurchase program, shares acquired			5,088,434	1,056,689
May 2014 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, approved amount		$ 50,000,000
Stock repurchase program, shares acquired		1,040,636
Stock repurchase program, average price per share (in dollars per share)		$ 48.07
Two Hundred Fifty Million Dollar Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, approved amount			$ 250,000,000
Stock repurchase program, shares acquired			4,196,349
Stock repurchase program, average price per share (in dollars per share)			$ 59.58